The present invention relates to a sensor for determining the mean value of the temperature of a heating area heated by a heat source, such as a glass ceramic hot plate, which is positioned between the heat source and the heating area and parallel thereto, the sensor comprising a ceramic element and a temperature-dependent resistor web attached to the ceramic body and the resistor web being positioned facing toward the heating area and at a distance thereto.
In typical electric stoves, particularly having a ceramic cooktop, one electromechanical protective temperature limiter is provided per heater to limit it to the maximum temperature. If the cooking platform is controlled using an electronic system, a substitution of the mechanical temperature limiter by electronic temperature sensors is possible, since the necessary circuit breaker (relay) is already provided. In the electronic control units used, a sensor is frequently also positioned in the region of the electronics of an electric stove.
For the operational reliability of the cooktop, it is important that these sensors are calibrated and thus detect the temperature of the particular cooktop reliably. However, the calibration of sensors requires a significant outlay and therefore causes significant costs. For example, resistance sensors must be trimmed into some sort of shape, this trimming not only causing additional costs, but rather also impairing the quality of the sensor and partially determining the size of the sensor.
A specific application of the present invention is the design and manufacturing of a resistance sensor, no further calibration steps having to be performed before it is installed in the cooktop. Resistors which are used for temperature measurement because of their defined temperature-dependent electrical conductivity characteristics are well-known. DE 3100852 reports on the use of temperature-dependent thin-film and/or thick-film resistors, positioned in the shape of a Greek key, for heating and/or temperature measurement purposes. In a special embodiment, the application of thin platinum or nickel webs to Al2O3 is suggested here. Further publications to be considered as prior art in this regard are, for example, U.S. Pat. No. 4,371,861 and EP 0063264. According to the present application, bringing sensors of this type as close as possible to parts which are heated directly or indirectly and whose temperature it is necessary to know is obvious. On the basis of these embodiments, WO 03/007660 describes a construction of a glass ceramic cooktop whose temperature is detected using a platinum resistance sensor of this type. Specifically, this invention claims a platinum resistor web for temperature detection, printed on a flat ceramic, which is positioned coplanarly to the heated glass ceramic area and in direct proximity thereto. However, it cannot be conclusively inferred from the embodiment specified therein how the temperature detection criteria required for cooktops per se are technically achieved using the platinum resistance sensor specified.
It would therefore be desirable and advantageous to provide an improved temperature sensor which obviates prior art shortcomings and is constructed compact enough to enhance a design freedom of a cooktop, while ensuring maximum operational reliability of the ceramic cooktop.